Short Answer:

Parting off is a machining operation performed on a lathe to cut off a finished part from the remaining workpiece or bar stock. It is done using a special narrow cutting tool called a parting tool, which moves radially into the rotating workpiece until it separates the required portion.

This process is commonly used in turning operations when several components are made from the same bar. Parting off provides a clean and accurate separation, reducing the need for additional cutting or finishing processes.

Detailed Explanation :

Parting Off

Parting off is an important lathe operation used to separate a finished part from the main workpiece. In this process, a thin cutting tool called a parting tool is fed radially into the rotating workpiece until the desired section is completely cut through. The tool is usually held in the tool post and aligned perpendicular to the workpiece axis to ensure a smooth and accurate cut.

The parting operation is also known as cutting off and is usually the final step in a turning process, especially when multiple identical parts are being made from one long rod or bar. It helps in achieving uniform lengths and accurate finishes.

Setup for Parting Off

Before performing the parting off operation, the setup of the workpiece and tool must be done carefully for safety and precision.

1. Mounting the Workpiece:
   The workpiece is held securely in the chuck or between centers to avoid vibration or movement during cutting.
2. Fixing the Parting Tool:
   The parting tool is fixed in the tool post so that its cutting edge is exactly at the center height of the workpiece. This alignment is important to prevent tool breakage or uneven cutting.
3. Speed and Feed Selection:
   A moderate spindle speed and suitable feed rate are selected depending on the work material and diameter. Too high speed may cause tool wear or poor finish, while too low speed can lead to rough cutting.
4. Lubrication:
   A cutting fluid or coolant is used to reduce friction, cool the tool, and flush away chips during operation.
5. Operation:
   The parting tool is slowly fed into the rotating workpiece until the tool reaches the center, and the part separates from the bar stock.

Working Principle

The working principle of parting off is based on the relative motion between the rotating workpiece and the stationary parting tool. The tool has a sharp cutting edge that penetrates the material due to the rotational motion of the workpiece. As the tool advances toward the center, the diameter of the cut reduces, and the chip flow becomes continuous until the part is completely separated.

The cutting speed and feed rate must be chosen carefully to ensure smooth chip removal. Using cutting fluids helps prevent tool overheating and ensures a fine surface finish.

Parting Tool

The parting tool is a narrow blade-like tool with a cutting edge at one end. It is made from high-speed steel (HSS) or carbide material to resist wear and withstand high temperatures. The tool’s cutting edge is ground with side clearance and rake angles to facilitate chip removal and minimize friction.

A properly ground parting tool provides a clean, accurate cut without bending or damaging the workpiece. The width of the parting tool determines the width of the cut (kerf) and should be as narrow as possible to minimize material waste.

Precautions During Parting Off

• The tool must be set exactly at the center height of the workpiece.
• The workpiece must be clamped tightly in the chuck to prevent vibration.
• Proper cutting fluid should be used to cool the tool and remove chips.
• The feed should be steady and not excessive to avoid tool breakage.
• The spindle speed should be reduced as the tool approaches the center to prevent chatter or tool jam.

Applications

Parting off is widely used in turning shops and manufacturing industries for the following purposes:

• Cutting off finished parts from bar stock.
• Producing washers, spacers, or rings of equal thickness.
• Separating several identical components made from one workpiece.
• Preparing the workpiece for further machining or assembly.

Advantages

• Produces accurate and smooth cut surfaces.
• Saves machining time by combining turning and cutting operations.
• Reduces material wastage due to the narrow cutting width.
• Suitable for high-speed production and repetitive operations.

Conclusion

Parting off is a vital lathe operation used to separate finished components from the remaining work material accurately. It uses a narrow parting tool that cuts radially into the rotating workpiece, ensuring precision and a clean surface. With proper tool alignment, speed, and lubrication, parting off can be done efficiently and safely, making it an essential process in modern machining and manufacturing.